Fuel cells feature high energy efficiency and very low CO2 emissions, and thus have been under vigorous technological development in recent years. Polymer electrolyte fuel cells (PEFCs) are the fuel cells using a polymer as an electrolyte. Due to their capability to operate under relatively low temperatures, the PEFCs are expected to be more progressively used.
FIG. 17 is a diagram showing a configuration of a typical conventional PEFC 100. As shown in FIG. 17, the PEFC 100 is formed by disposing a pair of current collectors 102 and a pair of insulating end plates 103, in this order, on the outer sides of a stack structure formed by stacking a plurality of cells 101, and fastening the resultant cell stack. The current collectors 102 each include a terminal 102a through which current is outputted.
Each cell 101 is formed by sandwiching a membrane electrode assembly (MEA) 104 by an anode side conductive separator 105 and a cathode side conductive separator 106.
In the MEA 104, a polymer electrolyte membrane 107 is sandwiched by an anode electrode 108 and a cathode electrode 109. The anode electrode 108 includes an anode side catalyst layer 108a and an anode side gas diffusion layer 108b. The cathode electrode 109 includes a cathode side catalyst layer 109a and a cathode side gas diffusion layer 109b. 
The anode side conductive separator 105 and the cathode side conductive separator 106 have grooves formed in a circumference of a center portion to be in contact with the MEA 104. The grooves are used to supply fuel gas to the anode electrode 108 and oxidant gas to the cathode electrode 109.
Generally, the stack structure of the cells 101 is fastened by a fastener band. FIG. 18 is a diagram showing a conventional cell module 200 disclosed in Japanese Patent No. 4656585 (patent document 1).
As shown in FIG. 18, in the cell module 200, end plates 203 are disposed on the outer sides of a stack structure in which unit cells 201 and barriers 202 are alternately arranged. The stack structure and the end plates 203 are fastened by a band 204.
Unfortunately, application of the fastening structure of the cell module 200 described in patent document 1 to the PEFC 100 shown in FIG. 17 still leaves room for improvement that higher performance is difficult to achieve.
Specifically, as one possible method for improving the performance of the PEFC 100 shown in FIG. 17, unevenness of the pressure applied to the MEA 104 from the anode side conductive separator 105 and the cathode side conductive separator 106 may be reduced. Thus, a uniform contact resistance is achieved, which in turn reduces unevenness in power generation distribution.
The method requires high strength and flatness of the end plates 103. Unfortunately, when the cell 101 is large, the end plate 103 with a large area is required, which is difficult to have large strength and high flatness.
When the end plate 103 is made by aluminum die-casting, high flatness cannot be achieved without secondary processing of machining a surface of parts obtained by the aluminum die-casting. Thus, the method requires high part manufacturing cost.
When the end plate 103 is made of a resin material, the high flatness is difficult to achieve after the end plate 103 warps.